1. Field of the Invention
High power elastic waves propagated in a liquid are used for destroying solid structures. This is the case in particular with renal or vesicle calculi.
For the method to be usable on biological tissues, it is necessary to be able to focus the wave in a precise point, so as to limit the energy density outside the zone of use and to reduce the risks of damage to the tissues through which it passes.
Now, it is known that the dimension of the focal spot is proportional to the wave length of the elastic wave, so to the duration of the wave front.
It is therefore indispensable, so as to obtain efficient focusing, to work with very steep wave fronts of the order of a microsecond, In this case, for example, the energy may be concentrated in a diameter of the order of 3 mm.
2. Descriprion of the Prior Art
To solve the problem of the generation of very steep wave fronts, it has been proposed to use either pin point elastic wave sources or distributed sources.
The pin point sources are formed either by a microcharge fired in the water, the explosion of which generates a spherical wave, or, as disclosed in DE. No. 2 722 252 (DORNIER), by discharging an electric arc between two immersed electrodes.
In both cases, the spherical wave generated is concentrated by an elliptic mirror. These solutions give poor control of the power and of the form of the wave produced and cause rapid wear of the parts which they require. The reliability is low, because the very high intensity at the level of a pin point source causes the appearance of disturbing phenomena.
Distributed sources have a large area, all the points of which vibrate in phase for generating a plane wave, which is concentrated either with an acoustic lens or by giving to the source itself the shape of a spherical skull cap.
They have a priori the advantage of limited fatigue because the energy density on the surface of the source is much lower than at the focal point.
The invention relates to a device which belongs to this category.
High power distributed source generators are already known for instance from SOURCES OF HIGH-INTENSITY ULTRASOUND (Volume 1) by L. D. ROZENBERG, Plenum Press, New York, 1969, in which the source is formed by a mosaic of piezoelectric elements. Their disadvantage is that their area must be considerable, because the power provided by each element is relatively small and because the electric generators required for energizing the elements must reach instantaneous powers of the order of a megawatt, which leads to high costs.
The invention provides a high power distributed source generator of much simpler construction.